Hamilton Island Landfill is a 240-acre site located in Skamania County in southwestern Washington. This site is owned and managed by the U.S. Army Corps of Engineers (USA/COE). From 1977 to 1982, this unlined landfill was used to dispose of approximately 19 million cubic yards of material excavated during the construction of a powerhouse for the Bonneville dam, which lies 1 mile upstream, as well as the debris collected during the demolition of a nearby town. Suspected chemical wastes included paints and degreasers. Approximately 900 people obtain their drinking water from wells located within 4 miles of the site. The Columbia River, a highly productive area for commercial and recreational fisheries, boating, sight-seeing, and wind surfing, is adjacent to the site. The site lies within a Federally-designated National Scenic Area.

Initial sampling indicated that surface and subsurface soil, groundwater, and leachate were contaminated with elevated levels of heavy metals including arsenic and cadmium, and various volatile and semi-volatile organic compounds (VOCs). A subsequent investigation determined, however, that hazardous substances at Hamilton Island did not pose a risk to human health and the environment.

Cleanup Progress: Construction Completed (No Further Action)

Early Actions: The U.S. Army fenced a portion of the site in 1987, restricting public access to the site and preventing direct contact with contamination.

Long-term Actions: In the fall of 1993, the U.S. Army began investigations into the nature and extent of site contamination. These investigations detected no hazardous wastes that required a cleanup action. Therefore, in March 1995, the EPA, the Washington Department of Ecology (WDOE), and the U.S. Army determined that no further action would be taken on Hamilton Island.